The present invention relates to a thermal recording head drive device used in a facsimile device or a printer. More particularly, the invention relates to a thermal recording head device of the type having electrodes extending, in a staggered manner, from a belt-shaped heat-generating resistive member.
In a conventional thermal recording head, especially in a line scanning thermal head, a belt-shaped heat generating resistive member is divided into a plurality of heat generating resistance elements, and video signal input leads, equal in number to the heat generating resistance elements, are arranged on one side of the belt-shaped heat generating resistive substrate. In this convention thermal head, if it is desired to record data with a high recording density and high quality, it is necessary to make the spacing between adjacent video signal input leads very small. As a result, it becomes difficult to connect the video signal input leads to the drive circuit.
In order to overcome the above-described difficulty, a thermal head as shown in FIG. 1 has been proposed. In FIG. 1, reference numeral 1 designates a substrate made of a ceramic plate or a substrate prepared by providing a heat sink of aluminum or copper on a ceramic base so as to provide suitable heat resisting and insulating characteristics and hence a suitable heat sinking action. Further, in FIG. 1, reference numeral 2 designates a belt-shaped heat generating resistive member which is formed using thin film, thick film or semiconductor techniques. The resistive member 2 is divided into a number of heat generating elements 2-1, 2-2, etc. corresponding to a predetermined number of recording positions. In order to improve the wear resistant property of the belt-shaped heat generating resistive member 2, a protective layer of glass, for instance, is formed on the member 2.
Further in FIG. 1, reference numerals 3 and 4 designate first and second lead groups which are used to supply current to the heat generating elements 2-1, 2-2, etc. The first lead group 3 includes leads 3-1, 3-2, etc., while the second lead group 4 includes a leads 4-1, 4-2, etc. These leads are arranged alternately on either side of the belt-shaped heat generating resistive member 2 in such a manner that the leads divide the resistive member 2 into the heat generating elements 2-1, 2-2, etc. with the elements 2-1, 2-2 being located between corresponding ones of the leads.
The thermal recording head described above has a number of alternate leads which serve as common leads for adjacent recording positions. Accordingly, the thermal recording head is advantageous in that the number of terminals on each side which must be connected to the drive circuit is reduced, and the spacing between leads is twice the size of the smallest dot which can be recorded.
In the conventional approach, the heat generating resistive element 2 is connected to the drive circuit as shown in FIG. 2. In FIG. 2, those components which have been described with reference to FIG. 1 are designated by the same reference numerals. In FIG. 2, reference numeral 5 designates a unidirectional element array, 6 video signal input gate array, 7 a video signal storing shift register, 8 power supply terminals, 9 video signal control terminals, and 10 a video signal input terminal.
If the power supply terminals 8-1 and 8-2 are simultaneously connected to the power source in the circuit described above and the video signal leads 4-1 is selected, for instance, both of the heat generating elements 2-1 and 2-2 generate heat. Therefore, the power supply terminals 8-1 and 8-2 must be separately connectable to the power source. Doing so effectively divides the heat generating element array into a first group of heat generating elements 2-1, 2-4, 2-5, 2-8, 2-9, etc. and a second group of heat generating elements 2-2, 2-3, 2-6, 2-7, 2-10, 2-11, etc.
In this arrangement, in recording one line, a printing operation including the following two steps must be carried out:
(1) Signals to be supplied to the heat generating elements 2-1, 2-4, 2-5, 2-8, 2-9, etc., for instance, are inputted to the shift register 7 through the video signal input terminal 10 while the powder supply terminal 8-1 is connected to the power source, thereby effecting printing of the picture elements corresponding to the elements 2-1, 2-4, 2-5, 2-8, 2-9, etc. PA0 (2) Next, signals to be supplied to the heat generating elements 2-2, 2-3, 2-6, 2-7, 2-10, 2-11 etc. are inputted to the shift register through the video signal input terminal 10 while the power supply terminal 8-2 is connected to the power source, thereby effecting printing of the picture elements corresponding to the elements 2-2, 2-3, 2-6, 2-7, 2-10, 2-11, etc.
As is apparent from the above description, in recording one line, it is necessary to input video signals to the shift register 7 in two steps. For this purpose, an external memory circuit which is adapted to store half the video signals for one line must be provided. This is a serious drawback in the conventional thermal recording head.
An object of the invention is thus to provide a thermal recording head device in which the need for such an external memory circuit is eliminated, and signal transmission between such an external memory circuit and the shift register is also eliminated, whereby the printing speed is increased.